Conventionally, carbamates (urethane compound) such as xylylene dicarbamate have been a useful organic compound as an industrial material having a wide range of applications such as a material of medicine, agricultural chemicals, and the like; a material of various fine chemicals; and furthermore, an analysis agent of alcohols.
Recently, such carbamates have been variously considered as a production material of an isocyanate without using phosgene.
That is, the isocyanate is an organic compound having an isocyanate group and is widely used as a material of polyurethane. The isocyanate is industrially produced by reaction between amine and phosgene (phosgene method).
However, phosgene is highly toxic, strongly corrosive, and disadvantageous in handling. Thus, as a method for producing an isocyanate instead of the phosgene method, a method for producing an isocyanate by thermally decomposing a urethane compound (carbamate) has been recently considered.
To be specific, for example, a method in which a formamide compound and dimethyl carbonate are allowed to react in the coexistence of methanol to extract the produced methyl formate to the outside of the system by distillation, while the obtained urethane compound is thermally decomposed to obtain an isocyanate compound has been proposed.
Patent Document 1 below has, for example, proposed that in a thermal decomposition reactor of such a urethane compound, a storage tank (material tank) of the urethane compound is in a nitrogen atmosphere and that the obtained urethane compound, when solid at normal temperature, is thermally melted to be stored from the viewpoint of workability at the time of being transported to the thermal decomposition reactor.
Also, as a method for producing an isocyanate instead of the phosgene method, in addition to the above-described method, Patent Document 2 below has, for example, considered a method of producing diisocyanate by synthesizing dicarbamate (urethane compound) by reaction of diamine, alcohol, and urea and/or a urea derivative and thereafter, thermally decomposing the obtained carbamate (urethane compound).